Did Earth once have two moons?

By: Mark Somerson

The Columbus Dispatch - September 08, 2011 10:30 AM

Some researchers believe that Earth once had two moons and the one we don't see any more is
splattered against the one we do.

Wow.

To find out the answer to that question and a zillion others, NASA is scheduled to launch
GRAIL, a
mission that will place two spacecraft into the same orbit around the moon. High winds forced NASA
to scrub the launch this morning. The agency has a couple of windows it is looking at on
Friday.

Here's how NASA describes what they'll do: "As these crafts fly over areas of greater and lesser
gravity, caused both by visible features such as mountains and craters and by masses hidden beneath
the lunar surface, they will move slightly toward and away from each other. An instrument aboard
each spacecraft will measure the changes in their relative velocity very precisely, and scientists
will translate this information into a high-resolution map of the Moon's gravitational field."